The invention concerns a method for producing a blow-molded container with a closable mouth section, a side wall, and a closed base.
The invention also concerns a blow-molded container with a closable mouth section, a side wall, and a closed base.
In container molding by the action of blowing pressure, preforms made of a thermoplastic material, for example, preforms made of PET (polyethylene terephthalate), are fed to different processing stations within a blow-molding machine. A blow-molding machine of this type typically has a heating system and a blowing system, in which the preform, which has first been brought to a desired temperature, is expanded by biaxial orientation to form a container. The expansion is effected by means of compressed air, which is fed into the preform to be expanded. DE-OS 43 40 291 explains the process-engineering sequence in this type of expansion of the preform. The aforementioned introduction of the pressurized gas comprises both the introduction of compressed gas into the developing container bubble and the introduction of compressed gas into the preform at the beginning of the blowing process.
The basic structure of a blowing station for container molding is described in DE-OS 42 12 583. Possible means of bringing the preforms to the desired temperature are explained in DE-OS 23 52 926.
Various handling devices can be used to convey the preforms and the blow-molded containers within the blow-molding machine. The use of transport mandrels, onto which the preforms are slipped, has proven especially effective. However, the preforms can also be handled with other supporting devices. Other available designs are grippers for handling the preforms and expanding mandrels, which can be inserted in the mouth region of the preform to support the preform.
The handling of containers with the use of transfer wheels is described, for example, in DE-OS 199 06 438 with the transfer wheel arranged between a blowing wheel and a delivery line.
The above-explained handling of the preforms occurs, for one thing, in so-called two-step processes, in which the preforms are first produced by injection molding and temporarily stored and then later conditioned with respect to their temperature and blown into containers. For another, the preforms can be handled in so-called one-step processes, in which the preforms are first produced by injection molding and allowed to solidify sufficiently and are then immediately suitably conditioned with respect to their temperature and then blow molded.
With respect to the blowing stations that are used, various embodiments are known. In the case of blowing stations that are arranged on rotating transport wheels, book-like opening of the mold supports is often encountered. However, it is also possible to use mold supports that can be moved relative to each other or that are supported in a different way. In stationary blowing stations, which are suitable especially for accommodating several cavities for container molding, plates arranged parallel to one another are typically used as mold supports.
Before a heating operation is carried out, the preforms are typically slipped onto transport mandrels, which either convey the preforms through the entire blow-molding machine or merely revolve within the heating system. In the case of vertical heating of the preforms in such a way that the mouths of the preforms are oriented vertically downward, the preforms are usually placed on a sleeve-like mounting element of the transport mandrel. In the case of suspended heating of the preforms, in which the mouths of the preforms are oriented vertically upward, expanding mandrels are usually inserted into the mouths of the preforms to clamp them tightly.
Blow-molded containers of this type are used in a great variety of designs for the packaging of products. In particular, containers of this type are filled with carbonated and noncarbonated beverages.
An important cost factor in the manufacture of these containers is the weight of the material that is used. For one thing, the material is relatively expensive and, for another, it is necessary to heat the material before the blow molding is carried out, and this requires considerable energy input. Accordingly, there is an ongoing effort to reduce the amount of material used and to form the blow-molded containers with walls as thin as possible.
Of course, reduction of wall thickness also leads to reduced stability of the containers. Therefore, the side walls of the container are provided with special ribbing. Efforts are also made to reduce the wall thickness in the area of the base of the container.
It is typically necessary to satisfy a number of requirements in the area of the side walls. On the one hand, the container needs sufficient stability in the longitudinal direction to enable it to absorb force loads during filling. On the other hand, consumers demand recessed grips to allow more secure gripping and handling of the bottle. However, these recessed grips reduce stability.